able ：最常用词，多用于褒义，着重指多方面的，经常性的，或潜在性的能力。有时也指高超、非凡的能力。
capable ：语气弱于able，指有能力、有潜力或有条件做某事，常与of连用。
competent ：强调具有能胜任某项工作的足够技能或其它所需的条件。
英语四级真题
This week's announcement of a new iPhone by a management team led by Tim Cook, who replaced Mr Jobs as chief executive in August, was generally regarded as competent but uninspiring.
出自-2012年12月阅读原文
Studies show they're also perceived as more competent than women in STEM Science, Technology, Engineering, and Mathematics fields.
2017年12月四级真题（第二套）阅读 Section C
英语六级真题
As a result, Black people are thought of a less competent and as having colder personalities.
出自-2015年12月阅读原文
As a result, " Black " people are thought of a less competent and as having colder personalities.
2015年12月六级真题（第一套）阅读 Section C
柯林斯高阶英汉双解学习词典释义
ADJ-GRADED
能胜任的;称职的
Someone who is competent is efficient and effective.